Our goal in this proposal is to define the molecular and cellular mechanism(s) of polyamine action and to develop new breast cancer treatments. Estrogen receptor (ER) and nuclear factor kB (NF-kB) are critical transcription factors in transmitting cell growth and survival signals. During the previous funding period, we found that the interaction of ER and NF-kB with estrogen response element (ERE) and NF-KB-response element (NRE), respectively, is facilitated by polyamines. Our hypothesis is that polyamines are positive regulators of ER and NF-KB function, and polyamine analogs interfere with the function of these transcription factors, induce apoptosis, and act in synergy with compounds that block ER or NF-KB. In Specific Aim 1, we will quantify the structure-activity relationship of polyamines in ER-ERE and NF-KB-NRE interactions by measuring DNA bending, binding constants, and the conformation and stability of proteins. These data will be used to select polyamine analogs for Specific Aim 2 to determine efficacy of cell cycle arrest and apoptosis of breast cancer cells. Preliminary results indicate that ERa and NF-kB pathways merge in regulating cyclin Dl and Bcl-2. We will investigate the role of polyamines in estrogenic activation of cyclin Dl and Bcl-2. The coordinate recognition of ERalpha, NF-kB. and coactivators by cyclin Dl and Bcl-2 promoters will also be examined. Results of these studies will be used to design strategies to combine polyamine analogs with inhibitors of ER or NF-xB function (Specific Aim 3). Synergistic growth inhibition and/or apoptosis observed in breast cancer cells will be validated in animal models (Specific Aim 4). Our studies will generate information on polyamine function in vitro and in vivo and advance development new therapies for breast cancer.